Background:

Systemic Lupus Erythematosus (SLE) is an autoimmune disease with many complications. SLE patients are at risk of osteoporosis (OP) and fractures due to the disease and/or long-term steroid use.

Objective:

To estimate in SLE females: 1) low bone mass prevalence and 2) fracture probability in those over the age of 40 using the Fracture Risk Assessment Tool (FRAX).

Methods:

271 SLE females with no OP fracture history were enrolled from 3 Canadian centres. Demographic data including age, SLE duration, body mass index (BMI), smoking status, OP risk factors, and medications were collected. Bone mineral density (BMD) of the lumbar spine, hip, and femoral neck were determined using DEXA. OP was defined as t-scores <-2.5 for those >50 years, and low bone mass as z-scores <-2 for those <50. For those >40, the 10 year probabilities of a major OP event (FRAX Major) and hip fracture (FRAX Hip) were calculated using age, sex, BMI, past fractures, family history, smoking, alcohol, presence of rheumatoid arthritis, steroid use and femoral neck BMD. Risks high enough to warrant pharmacological treatments are >20% for FRAX Major and >3% for FRAX Hip.

Results:

Subjects had a mean (SD) age of 43.8 (13.1) years, SLE duration of 11.6 (10.4) years, BMI (kg/m2) of 26.3 (6.3), 57% consumed alcohol, 44% were smokers, 38% were postmenopausal, 28% had a prior fracture, 24% were on steroids >7.5 mg, and 41% were on steroids for at least 3 months. Calcium and vitamin D were used by 48% and 39% respectively. There was a significant correlation between BMD of the femoral neck (r=-0.26, p=0.001) and hip (r=-0.35, p<0.01) with the duration of steroid use.

In females >=50 years (32.8%), the mean t-scores of the spine, hip, and femoral neck were -0.73, -0.52, -0.78 respectively. OP was diagnosed overall in 4.8%, and in 11.5%, 4.2%, and 5.7% in spine, hip, and femoral neck respectively.

In females <50 (67.2%), the mean z-scores of the spine, hip, and femoral neck were -0.22, 0.11, and -0.19 respectively. Low bone mass was at the spine, hip, and femoral neck in 52.7%, 39%, and 2.8% of the participants.

Overall, there was no difference in BMDs based on calcium and vitamin D intake. However, spine BMD was significantly lower in those who took steroids longer than 3 months [1.1 (0.1) vs. 1.0 (0.1), p=0.006].

Of those >=40 (63.5%), the mean FRAX Major was 10.2% (6.3) and FRAX Hip was 1.8% (3.3). FRAX Major >=20% was seen in 7% (n=12) of whom only half were on OP treatment. FRAX Hip >=3% was noted in 15.8% (n=27) where 2/3 were on treatment. OP treatment was given to 22% and 16.7% of females who had low FRAX Major (<20%) and FRAX Hip (<3%) scores respectively. FRAX Major correlated significantly with: steroid duration (r=0.31, p=0.03) and age (r=0.21, p=0.01). Similarly, FRAX Hip correlated significantly with: steroid duration (r=0.32, p=0.03), age (r=0.23, p=0.01), and SLE duration (r=0.20, p=0.01).

Conclusion:

Low bone mass is prevalent in SLE females without prior OP fractures. This is important for females <50 years, where routine BMD monitoring is not currently part of standard care. FRAX scores may provide additional insight to the level of risk and identify those who may benefit from OP treatments. This may help reduce future morbidity and mortality.